The 16 wheels that you have center on the hub (hub-centric) while the 16.5 wheels are lug-centric. The "swiveling" lug nuts have a rotating washer integrated with the nut. I think this allows the wheel to more easily center on the hub. I think the remaining question is whether or not your hubs are suitable for hub-centric wheels. Maybe someone else will know. If you live near a Costco with a tire shop, they sell lug nuts cheaper than anywhere else. They have quite a selection but I'm nut sure if they have the swivel ones.